For filling a repair material into a defective part of a tooth or covering a defective part of a tooth with a repair material, a dental adhesive is usually used. Known dental adhesives include one containing a compound having a polymerizable group and a phosphoric acid group.
For example, Japanese Laid-Open Patent Publication No. 2006-76973 (patent document 1) reports that a photopolymerization type adhesive for tooth structure adhesion which contains an acidic group-containing radically polymerizable monomer having a methacryloyl group and a phosphoric acid group, like 2-methacryloyloxyethylphosphoric acid, has a high tooth structure adhering performance to enamel and dentin. However, the bond strength was not necessarily high enough.
The Journal of Japanese Society for Dental Materials and Devices Vol. 17, No. 2 120-125 (1998) (non-patent document 1) discloses an N-methacryloyl-ω-amino acid which has a methacryloyl group in the molecule and is an amino acid derivative differing in the length of methylene chains (hereinafter, this may be abbreviated as “NMωA”). It is reported that when this NMωA is caused to apply as a primer on dentin collagen, the interaction between the NMωA and the dentin collagen increases and the bond strength between the dentin and a composite resin is improved as the methylene chain length of the NMωA increases. However, the improvement of materials with respect to bond strength has been desired.
When such a dental adhesive has been applied to the dentin, it is important for the adhesive to have a decalcifying function of dissolving the dentin surface with an acidic component, a permeating function that a monomer component permeates the collagen layer of the dentin, and a curing function that the permeating monomer component hardens to form a hybrid layer (hereinafter, this may be called “resin impregnated layer”) with collagen.
Heretofore, there has been studied the simplification of the usage mode of dental adhesives from the three-bottle, three-step type in which the decalcifying function, the permeating function and the curing function are applied successively to the two-bottle, two-step type in which the decalcifying function and the permeating function are united, and further to the one-bottle, one-step type in which all the decalcifying function, the permeating function and the curing function are united. Compounds which can be used as dental adhesives which exert excellent adhesive properties in any usage mode have been desired.
Compounds having an amide bond or an ester bond, including the above-mentioned compound which can be used as a dental adhesive, are often important in view of their functions. As the method for synthesizing such a compound, there have been reported, for example, a method by which a compound having an amide bond is produced from a carboxylic acid and an amine by using a carbodiimide-based condensing agent represented by dicyclohexylcarbodiimide (hereinafter, this may be abbreviated as “DCC”), and a method by which a compound having an ester bond is produced from a carboxylic acid and an alcohol.
For example, Japanese Laid-Open Patent Publication No. 2004-131468 (patent document 2) discloses a method by which a carboxylic acid and an alcohol are caused to undergo dehydration condensation by using DCC to produce an acrylic acid ester phosphonic acid.
However, there are the following problems with methods using carbodiimide-based condensing agent represented by the DCC: (1) when there is a large amount of water in a reaction system, the proceeding of the reaction is inhibited. (2) When an alcohol is used as a reaction solvent, a side reaction, namely, condensation of the alcohol and a carboxylic acid, occurs. (3) When a carboxylic acid or an amine has a free hydroxyl group, a side reaction, namely, condensation of the free hydroxyl group and the carboxylic acid, occurs. (4) DCC tends to react with both a carboxylic acid and an amine. Therefore, DCC and the carboxylic acid are usually caused to react first, followed by addition of the amine. However, the yield of a compound having an amide bond may decrease depending upon the timing of the addition. (5) A care should be exercised in handling a carbodiimide-based condensing agent because it is prone to cause skin irritation.    Patent document 1: Japanese Laid-Open Patent Publication No. 2006-76973    Patent document 2: Japanese Laid-Open Patent Publication No. 2004-131468    Non-patent document 1: the Journal of Japanese Society for Dental Materials and Devices Vol. 17, No. 2 120-125 (1998)